1. Field
Exemplary embodiments of the present invention relate to an image sensor and a method of operating the same.
2. Description of the Related Art
Recently, a demand for a digital camera module has increased with the development of image communications using the Internet.
The digital camera module includes an image sensor. The image sensor is a device that converts an optical image into an electrical signal. As the image sensor, a charge coupled device (CCD) and a complementary metal-oxide-semiconductor (CMOS) image sensor have been widely used.
The CCD has disadvantages in that a driving method is complicated, power consumption is increased, a process is complicated due to many mask processes in a manufacturing process, and a signal processing circuit may not be implemented within a chip to have a difficulty in implementing a one-chip. On the other hand, a CMOS image sensor has been more spotlighted recently, since control circuit, driving circuit, and signal processing circuit are integrated on a single chip as a monolithic IC. In addition, the CMOS image sensor may be more economically competitive than the existing CCD, due to a low voltage operation, low power consumption, compatibility with peripheral devices, and utility of a standard CMOS manufacturing process.
One of the criteria for indicating performance of the image sensor is a dynamic range. The dynamic range generally represents a maximum range that may process a signal without distorting an input signal. As the dynamic range is increased, the image sensor may obtain a good image, regardless of whether brightness is widely changed.
The dynamic range of the image sensor is in proportion to an amount of data to be processed by the image sensor. However, the amount of data that may be processed by the image sensor is limited, so that the image sensor may not represent all the dynamic ranges of the natural world. When the dynamic range of the image acquired by the image sensor is insufficient, a histogram of an image is biased to a dark area or a bright area, so that light may be saturated. Meanwhile, even when portions having actually different brightness are present in the acquired image, a dark area is biased to a narrow dynamic range or light is saturated in a bright area, so that it may be difficult to differentiate objects within the image. In severe cases, even though objects are actually present, objects may not be seen due to an insufficient dynamic range.
The image sensor integrates photo charges generated in response to light incident through each pixel included in the image sensor to convert an optical signal into an electrical signal, thereby acquiring an image. The image sensor generally acquires an actual appearance of the natural world as is, but may acquire a darker or brighter image than an actual image based on integration time within which light is collected. That is, as the image sensor collects light for a long period of time, the image sensor may obtain a brighter image. Therefore, the integration time of the dark area is short, and when an image is too bright, it may be considered that the integration time of the saturated area is increased.
A method for extending the dynamic range of the image sensor may refer to Korean Patent Application No. 10-2007-0064613 (entitled as “method and apparatus for improving dynamic range of images”, which is incorporated herein by reference in its entirety) and the like. Korean Patent Application No, 10-2007-0064613 discloses a method for extending a dynamic range of an image acquired by an image sensor using a nature in which the gradation expression of a dark area is abundant with the increased integration time of light (or, photo charge) and the gradation expression of a bright area is abundant with the reduced integration time of light.
Describing in more detail, in an image sensor including a pixel array in which a plurality of pixels are disposed in a matrix form, the integration time of pixels of some rows (hereinafter, referred to as “first rows”) is set to be long and the integration time of pixels of the remaining rows (hereinafter, referred to as “second rows”) adjacent to some rows is set to be short. Further, the image sensor stores pixel data of the first rows and pixel data of the second rows and interpolate the data to generate new data configuring an image, thereby obtaining the advantages when the integrated time is increased and when the integrated time is reduced.
However, to interpolate the pixel data included in one row and the pixel data included the other row, the image sensor generally stores the pixel data included in two rows and calculates the data, thereby generating new data. Therefore, the image sensor has concerns in that the chip size is increased due to the memory for storing data and the time to acquire the image data is increased due to the increased calculation time.